The present invention relates to a control apparatus for an internal combustion engine, and in particular, to a control apparatus suitably applicable to an internal combustion engine that performs both knock control for adjusting an ignition timing and a variable valve actuation control for an engine valve in accordance with the occurrence of knocking.
In an internal combustion engine, depending on its use, deposits originating from an unburned fuel, a blow-by gas, a lubricant, or the like may be gradually deposited on an intake port, an intake valve, a piston, or the like. It is known that such an increase in the amount of deposits leads to, for example, a decrease in the substantial volume of a combustion chamber and an associated increase in in-cylinder compression pressure during burning, thus increasing the possibility of knocking.
In general, for the internal combustion engine, knock control is preformed to detect the occurrence of knocking using a knock sensor and adjust the ignition timing on the basis of the results of the detection. The knock control suppresses the occurrence of knocking by retarding the ignition timing when the incidence of knocking is high, while advancing the ignition timing when the incidence is low.
On the other hand, in recent years, internal combustion engines with a variable valve actuation mechanism that can vary the valve actuation of engine valves, that is, intake or exhaust valves, have been put to practical use, for example, a variable valve timing mechanism that can vary a valve timing for the engine valves and a variable valve lift mechanism that can vary the valve lift amount of the engine valves. Such an internal combustion engine with a variable valve actuation mechanism can reduce the actual compression ratio of the engine by adjusting the valve actuation of the engine valves. Thus, the internal combustion engine with the variable valve actuation mechanism can also suppress the occurrence of knocking by allowing the variable valve actuation mechanism to reduce the actual compression ratio to prevent an increase in in-cylinder compression pressure caused by deposits.
Thus, in the prior art, a control apparatus for an internal combustion engine has been proposed which performs knock control for the ignition timing based on the results of the detection by the knock sensor and which also allows the variable valve actuation mechanism to perform the variable control of the valve actuation on the basis of the results of the detection by the knock sensor as set forth in Japanese Patent Laid-Open No. 8-338272.
With the control apparatus described in Japanese Patent Laid-Open No. 8-338272, the ignition timing is retarded on the basis of the detection of the occurrence of knocking by the knock sensor. On the other hand, the amount of retardation of the valve timing for the intake valve carried out by the variable valve timing mechanism is set in accordance with the intensity of the knocking detected by the knock sensor. Such a control apparatus can effectively inhibit the occurrence of knocking on the basis of the multiplier effect of the retardation of the ignition timing and the valve timing.
Once the ignition timing has been changed by the knock control, the appropriate values of the valve actuation of the engine valves are also changed. Thus, once the ignition timing and the valve actuation have been individually changed as in the case of the above conventional control apparatus, the set values of the valve actuation may deviate from the appropriate values in the present engine operating state. As a result, the performance of the engine otherwise successfully provided may not be adequately enjoyed to its limit. Thus, although the conventional control apparatus is effective on the inhibition of the occurrence of knocking, the valve actuation is not sufficiently optimized so as to deal with changes in engine operating state accompanying changes in ignition timing. Therefore, the conventional control apparatus still has room for improvement in terms of mileage or the like.